Interpretive Summary: Fungal and bacterial diseases of cultivated crop plants cause huge losses in agricultural productivity. Certain fungi adversely affect human and livestock health by producing toxins in the affected grain and feed crops. In collaboration with the agricultural biotechnology industry, we studied the antimicrobial effects of a small protein called a peptide. We demonstrated that the synthetic peptide, D4E1, possesses a broadspectrum antimicrobial effect against several fungal and bacterial pathogens that affect crop productivity, and causes food and feed safety-related concerns due to mycotoxins. Previous research has shown that the D4E1 gene, when introduced into plants, provides built-in resistance to fungal diseases. Taken together, genetic modification of crop plants with this peptide has great utility in protecting plants against devastating microbial pathogens without using chemical fungicides.